Cannot UNCHECK 'Ask to save logins'
I use Firefox on multiple devices with synch. I don't want Firefox to ask to save logins, never ever anywhere. :) On my laptop, the option is greyed out and checked, i.e. set to ask to save passwords. So this settings syncs to the other PC's. When running about:config and looking at the option there, it is set to true and also here set to true without possibility to change.
That may have been set by your distro. You could check in about:policies. It may instead have used autoconfig.
You can try Firefox from the official Mozilla server if you currently use a version from the repositories of your Linux distribution to see if it behaves differently.
Thanks for your replies. The issue is actually on my Windows 10 laptop, I just wrote it from my Linux workstation (where I can uncheck the option, which unfortunately reverts to checked by syncing to my laptop...). But I think I found the issue in about:policies, where "PasswordManagerEnabled" is set to true. However, I have no password manager and never used one, so need to figure out why this is....
You might have to go back to original computer and all devices and remove the sync on each to see if you get that option back.